I'm lucky to have a friend who is a picture framer by trade and he gave me lots of picture mounts in lots of different sizes and shapes. I put some of these to good use by stapling them onto the shed wall to offer a more interesting and welcoming surface and encourage experimentation.
The paint pots are held in the plastic clips used for holding drain pipes against the wall, which perfectly fit cups for the paint and are easily screwed into the wood of the shed. No more spilled paint.
The children know that they are allowed to paint anything in this area, gravel, leaves, rocks, even the roof of the shed if they can reach it, but they also know not to paint anywhere else. They have tested these boundaries by moving around the shed to other sides and to other parts of the garden but now they know, they are happy to keep to their side of the bargain.
We don't worry about keeping the colours pure, we even top up colours with other colours and somehow we don't seem to end up with everything a muddy brown. The paint soon dries and the next layers goes on fresh and bright.
If it rains and the paint pots fill with water they use that to get different effects. One little boy even worked out that he could use the paint as glue and stuck leaves on the wall... child led learning at it's best.
I'd love to hear your comments on how else you think I could improve this area or anything else I could offer or just your experiences of similar experiences. :-)